1. Field of the Invention
The present invention relates to an actuator control circuit which makes it possible to control, for example, the displacement speed of an actuator such as a cylinder.
2. Description of the Related Art
In recent years, an pneumatic actuator, for example, a cylinder is widely used to transport a small object or the like especially in electronic and electric industries as well as in other industries. The cylinder includes a piston which makes rectilinear reciprocating movement along a cylinder chamber of a cylinder tube. Concerning such a cylinder, those generally known to be used when the displacement speed of the piston is controlled include a meter-in circuit 1 (see FIG. 19) which controls the flow rate of the pressure fluid flowing through a passage disposed on the supply side for supplying the pressure fluid into the cylinder chamber, and a meter-out circuit 2 (see FIG. 20) which controls the flow rate of the pressure fluid flowing through a passage disposed on the discharge side for discharging the pressure fluid from the cylinder chamber.
In FIGS. 19 and 20, reference numeral 3 indicates a speed control valve comprising a check valve 4 and a variable throttle valve 5. Reference numeral 6 indicates a switching solenoid-operated valve. Reference numerals 7a and 7b indicate first and second cylinder chambers respectively.
However, for example, when a pneumatic actuator such as a cylinder is operated at a low speed in order to transport, for example, a small object or the like, if the meter-in circuit 1 is used, then the displacement state and the stop state are intermittently repeated. As a result, an inconvenience occurs in that the so-called stick-slip phenomenon takes place, in which a step-shaped characteristic curve appears, which represents the relationship between the time and the displacement amount.
Further, the meter-in circuit 1 concerning the conventional technique is inconvenient in that the so-called delay of response time occurs, in which the time required to start the displacement of the piston is delayed when the operation of the cylinder is started again after the operation of the cylinder is stopped for a long period of time.
On the other hand, the meter-out circuit 2 is inconvenient in that the so-called jumping out phenomenon occurs, in which the piston makes quick displacement along the cylinder chamber 7a (7b) due to any adhesion of the piston when the operation of the cylinder is started again after the operation of the cylinder is stopped for a long period of time.